This invention relates generally to automobile lifting jacks, and more particularly to a screw jack.
Automobile lifting jacks heretofore have been generally of the single leg ratchet type having a strut member provided with ratchet teeth engaging a load-bearing movable member which is moved upwardly and downwardly upon the strut member by manipulating a ratchet mechanism. While this type of automobile lifting jack is generally sufficient, it has the distinct disadvantage of providing only incremental adjustment during the lifting of the automobile, this adjustment corresponding to the space between the teeth formed on the strut member. Furthermore, should one of the teeth fracture from the strut member there is the possibility of the entire automobile collapsing and injuring someone.
To provide a more reliable jack arrangement, a screw jack has been utilized. The screw jack incorporates a hollow strut member having a threaded shaft extending therethrough and which shaft passes through a threaded element engaging the load-bearing member of the jack to raise and lower an automobile while the threaded shaft is turned. While this type of automobile lifting jack provides continuous adjustment between its lower and upper limits they have been relatively expensive and complicated to manufacture. Also, in some instances screw jacks for automobile use have required two or three supporting legs in addition to the strut member for sufficient rigidity to prevent the automobile from falling off the jack. While single leg screw jack configurations have been developed in the past and provide substantial improvements over prior art type bumper jacks of both the ratchet and multi-leg screw types, they are relatively expensive to manufacture.